The invention relates to a system for adjusting a transmission gear ratio.
From the state of the art, many possibilities are known to adjust the gear ratio of a motor vehicle transmission to adjust a specific desired rpm of the vehicle motor. In U.S. Pat. No. 4,893,526, a desired output torque is determined from the vehicle longitudinal speed and the position of the accelerator pedal actuated by the driver. Thereupon, a desired value for the engine rpm is determined in dependence upon the desired output torque and the vehicle longitudinal speed. This desired value for the engine rpm is controlled by the adjustment of a continuously variable vehicle transmission. Furthermore, the desired output torque as well as the adjusted transmission gear ratio are applied to adjust the engine torque.
WO 95 20114 A discloses a control for an automatic motor vehicle transmission wherein the engine rpm is intended to be adjusted to the region of optimal efficiency, minimal exhaust-gas emission or maximum power via a fuzzy logic control circuit by a continuous control of the transmission ratio. Here, the efficiency of the vehicle engine is of primary concern. The influence of the transmission efficiency on the total efficiency of the drive train is not considered.
The object of the present invention is to adapt the engine rpm optimally to the particular driving situation or the particular driving state. This engine rpm can be controlled by an adjustment of the transmission gear ratio.
The invention proceeds from a system for adjusting a motor vehicle transmission which is changeable in its transmission gear ratio. The transmission has an efficiency characteristic which is dependent upon the transmission ratio. A first quantity, which represents the actual transmission output rpm, is detected as well as a second quantity, which represents a desired value for the drive torque. A desired rpm of the vehicle engine is determined at least in dependence upon the detected first quantity and the determined second quantity and in dependence upon the efficiency characteristic. The adjustment of the transmission ratio takes place in dependence upon the desired rpm of the vehicle engine which is so determined.
For a drive torque wanted by the driver, an optimal transmission ratio and the required engine output torque are determined via a coordinated drive train control. The components xe2x80x9cenginexe2x80x9d and xe2x80x9ctransmissionxe2x80x9d of the drive train are correspondingly driven so that the required drive torque is made available. The invention permits a systematic consideration of the transmission efficiency for the determination of the optimal transmission ratio. In this way, a maximization of the total efficiency of the drive train is achieved for an optimal vehicle operation. The advantage resulting therefrom is the basic possibility to better adapt the drive train to the requirements via optimization of the total efficiency, the torque reserve and/or other optimization criteria.
It is especially advantageous when the determination of the desired rpm of the vehicle engine takes place in such a manner that a desired rpm is determined for the combinations of the detected first and the determined second quantities. For this desired rpm, at least one vehicle engine parameter (such as fuel consumption, torque reserve and/or exhaust-gas emission) is optimized in the sense of a minimum or maximum.
The determination of the desired rpm can take place by means of at least one characteristic field.
Advantageously, the torque amplification characteristic and/or the efficiency characteristic of the transmission for different transmission gear ratios are applied to determine the desired rpm of the vehicle engine or for determining the characteristic field.
The torque amplification and/or efficiency characteristics can, in general, include the torque amplification and/or the efficiency of the transmission in dependence upon the first and second quantities. Here, the torque amplification and/or efficiency characteristics are advantageously in the form of characteristic fields.
Especially for a transmission, which is continuously variable with respect to its transmission ratio, it is provided that the determination of the desired rpm of the vehicle engine or the determination of the characteristic field takes place in such a manner that the corresponding torque amplifications and/or efficiencies of the transmission are determined from the existing characteristic fields of the transmission (torque amplification and/or efficiency characteristics) for different transmission ratios. An interpolation is then made between these determined torque amplifications and/or efficiencies.
In an especially preferred embodiment of the invention, it is provided that the parameter of the vehicle engine, which is to be optimized, is present as an engine characteristic field in dependence upon at least the engine rpm and the engine output torque. The procedure according to the invention is then as follows:
For different transmission gear ratios, the corresponding torque amplifications and/or the corresponding efficiencies are determined to different first and second quantities by means of the torque amplification and/or efficiency characteristics. The engine output torques, which belong to the first quantity, are determined for the different transmission gear ratios while considering the determined corresponding torque amplifications and/or the corresponding efficiencies. Values of the parameter to be optimized are determined by means of the present engine characteristic field and the values determined in this manner are applied for the determination of the desired rpm of the vehicle engine.
The second quantity, at least in pregiven operating states, is preferably determined in dependence upon a quantity which represents the position of the accelerator pedal actuated by the driver. The vehicle engine parameter, which is to be optimized, can be designed so as to be selectable.